The internet was totally grossed out recently by images that showed a McDonald's hamburger sitting out in the open for six months without decomposing or rotting. But one blogger dug a bit deeper, and it turns out no hamburgers rot.

Sally Davies bought a McDonald's Happy Meal on April 26, 2010. She placed it on her coffee…
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Well, no burgers that are roughly the shape and size of McDonald's plain burger, anyway. J. Kenji Lopez-Alt over at Serious Eats was tired of people slagging off the Happy Meal burger without any real scientific sense of what was going on. The Happy Meal burger doesn't rot, sure, but he wanted to know why it doesn't rot.

To figure out just that, Lopez-Alt set up a little experiment. He'd leave a Happy Meal burger out, unwrapped, just like the previous slideshows had shown. But he'd also make his own burger out of ground chuck and put it on a store-bought bun and leave that out too. And along with those two he'd whip up pretty much every variation on the theme:

Sample 1: A plain McDonald's hamburger stored on a plate in the open air outside of its wrapper.
Sample 2: A plain burger made from home-ground fresh all-natural chuck of the exact dimensions as the McDonald's burger, on a standard store-bought toasted bun.
Sample 3: A plain burger with a home-ground patty, but a McDonald's bun.
Sample 4: A plain burger with a McDonald's patty on a store-bought bun.*
Sample 5: A plain McDonald's burger stored in its original packaging.
Sample 6: A plain McDonald's burger made without any salt, stored in the open air.
Sample 7: A plain McDonald's Quarter Pounder, stored in the open air.
Sample 8: A homemade burger the exact dimension of a McDonald's Quarter Pounder.
Sample 9: A plain McDonald's Angus Third Pounder, stored in the open air

Rigorous! So what happened? Did the regular "real" burgers shrivel up into a moldy beef balls while the Mickey D's chemical pucks remained impervious to bacteria?

Nope. None of the skinny burgers showed signs of rot. It was only the quarter pounders—both the McDonald's one and the homemade one—that got funky. So the no-rot phenomenon isn't a matter of substance, Lopez-Alt concluded, but rather one of size:

The burger doesn't rot because it's small size and relatively large surface area help it to lose moisture very fast. Without moisture, there's no mold or bacterial growth. Of course, that the meat is pretty much sterile to begin with due to the high cooking temperature helps things along as well.

And what about when you put a Happy Meal burger in a bag, where the moisture can get trapped?